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Wanted: A Very Accurate Timer

Discussion in 'Electronic Repair' started by [email protected], Jun 24, 2005.

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  1. In the UK, the mains frequency might well average out at 50 Hz over 24
    hours, but that's not the same as being absolutely accurate over any 6
    hour period. Can't see the US being any different.
     
  2. NSM

    NSM Guest

    Hard to take a show seriously where spacecraft make banking turns in space
    and go "Whoosh" as they pass you. "Blake's 7" at least got that part right.

    N
     
  3. Peter Duck

    Peter Duck Guest

    In message <>
    I've a radio-controlled clock and a nominally-50Hz-driven one in the
    same room.
    There's only any point in synchronising them early in the morning: that
    way, they'll agree again every morning, i.e. the 50HZ is carefully kept
    to be *on average* true, but by evening, especially in winter, the
    difference can be as much as 20 seconds.
    Nor can I ...
     
  4. 2.com

    2.com Guest

    Thanks for all the responses.

    I originally entertained something like this 2-1/2 years ago, but the
    timer I needed, which was basically a racing watch, but with a large
    bright red display, was not commercially available and proved too
    complicated to build.

    So I have to settle on just a simple timer for now, and worry about
    getting something more complex later.

    It is way too complicated to go into the details as far as why I need
    this, but basically this will involve conducting experiments/tests on
    the accuracy of human timing, and also the confirmation of certain
    conclusions drawn from studying the code contained within the hardware
    I'll be testing against.

    1/60th of a second is important because it is specific to that hardware
    and how it functions. It uses registers that change every 1/60th of a
    second to make certain occurances "random". If one could react with an
    accuracy of 1/60th of a second, then these occurances would follow a
    predictable pattern. But of course that kind of timing is not humanly
    possible with any kind of consistency.

    Anyway, to simplify what I'm doing, this involves a huge number of
    timed inputs(by a person) over the course of several hours. The timer
    will be the reference.

    If it is easier for me to get a set-up that involves frequent
    resets/corrections to get the needed accuracy at any 60th of a second
    over the course of several hours, then that is what I'll have to do.

    P.S: The hardware itself is a videogame.

    Darren Harris
    Staten Island, New York.
     
  5. Richard H.

    Richard H. Guest

    This strikes me as a very different definition of the problem from your
    original post...

    If your goal is to have an event 60 times per second with good accuracy,
    that is trivial with most microcontrollers. Even a basic design could
    get you 100,000 events per second with good accuracy.

    But what you described in your original post was a requirement to finish
    after 6 hours with a clock drift of no more than 1/60 second. That
    problem is 21,600 times harder, and requires elaborate solutions.

    i.e., it sounds like your requirement is for a timer that can:
    a) trigger 60 times per second with "good" accuracy
    b) count for 6 hours or more

    In defining "good" accuracy, 1% equates to +/- 0.00017 secs margin per
    60/sec event (between 0.01649 and 0.01683 seconds per event). These
    timings aren't likely to vary much on one board (barring temerature
    changes), but would vary in this range from one board to the next.

    So, what degree of accuracy are you really needing?

    Cheers,
    Richard
     
  6. 2.com

    2.com Guest

    How? In my original post I said the following: "It must to be accurate
    to within 1/60th of a second over the course of 6 hours."
    But that is not my goal.
    Still wrong. The timer will trigger nothing. All it needs is a display
    so that I can see the seconds.(Though showing 1/60th of a second
    intervals would be great, it's just not required for this project,
    which I have had to simplify greatly).
    1/60th of a second...

    (ie: When the 2 hour, 53 minute, and 37 second point is reached, the
    display should show it at exactly that time at an accuracy of 1/60th of
    a second from when the clock started running).

    Darren Harris
    Staten Island, New York.
     
  7. Mike Monett

    Mike Monett Guest

    2.com wrote:

    [...]
    You have no idea what your requirements mean. A drift of 1ppm in 6 hrs is
    meaningless in a marathon or other race, when the wind can easily cause
    1% change in performance.

    So in Brooklanese -Fahgettaboutit!

    Mike Monett
     
  8. 2.com

    2.com Guest

    There is no wind involved here.

    I've been trying not to get into the details, because details lead to
    the request for more details, and this is just way to complex to get
    into here. Not just as far as what I'm doing, but the timer I am
    seeking is actually inadequate for all of the experiments I want to do.

    Now if this is so difficult to understand, then the more complex timer
    will be near impossible to explain.

    For this project there will be 1,296,000 increments over the course of
    6 hours. I just need the option of *visually* seeing on the timer's
    display when each second increments beginning with the press of a start
    button, and the accuracy must be 1/60th of a second at worst for any of
    those 21,600 seconds after zero.(I'm assuming that the timer will have
    to be plugged in an AC outlet).

    Darren Harris
    Staten Island, New York.
     
  9. Mike Monett

    Mike Monett Guest

    2.com wrote:

    [...]
    I think you just lost the interest of anyone capable of helping you.
    The truth you seek is out there. Have fun:)

    Mike Monett
     
  10. quietguy

    quietguy Guest

    Have a think about it and perhaps that will simplify your problem

    David
     
  11. 2.com

    2.com Guest

    Well compensating for centrifugal force is plausible, and space is not
    a complete vacuum. :)

    Darren Harris
    Staten Island, New York.
     
  12. 2.com

    2.com Guest

    No. I'm sure that accuracy is definitely what is needed.
    The problem is what it is. There is nothing that can be changed.

    Obviously, even this simple version of a timer is not commercially
    available, and not something that can be easily built.

    Thanks.

    Darren Harris
    Staten Island, New York.
     
  13. Jim Adney

    Jim Adney Guest

    Oops, I'm off by one decimal place; it's more like one part in 1.3
    million. This can be done with a good crystal oscillator, but it's got
    to be a pretty good one, and it has to be calibrated against a real
    standard.

    The question remains of why one would need this degree of accuracy in
    a timing function.

    -
     
  14. James Waldby

    James Waldby Guest

    You will waste a lot less of everyone's time if you just go ahead
    and explain what you want. If you happen to know. Of course if you
    don't know what you want, you are less likely to get it.

    Anyhow, AIUI you have a video game and you want to use a timer for
    doing something related to this game ... perhaps you want to reverse
    engineer it, perhaps crack some protection, perhaps set up a computer-
    aided play device. Whatever. And you think that having a timer with
    1/60 second accuracy displaying the current time throughout a six hour
    period will help you do so. (It may be silly for you to think so, because
    if you are just reading the time off the running display or pushing
    buttons to record the time when stuff happens, you won't be able to do
    either one with 1/60 second reaction times anyway.)

    Note that the clock in the video game almost certainly will drift
    around in a range at least 10 parts per million wide, which makes
    your 1 ppm requirement superfluous. Instead, snoop the video game
    clock and use a buffered copy of it to drive the counters in your timer.
    This way your displayed time always is in sync with the video game time.
    Perhaps your problem is that you don't know what you are doing.
    Feel free to convince us otherwise.
    As several people have noted, you could use a TXCO (temperature
    compensated crystal oscillator) or a crystal oven for adequate
    performance. See eg $4 and $18 items
    http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7526666127
    http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7526612301

    Note that you can get an inexpensive counter/timer on ebay, like
    http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7526025102
    http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7526108906
    http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7526165454
    http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7526085126
    http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7526393893
    http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7525744632
    The bench instruments probably have 7 to 10 digit stability
    when warmed up and similar accuracy when in cal. Some of them
    might make their timebases externally available and/or have
    totalizer functions that would do the job for you. In any case,
    if you build a TXCO you'll need a counter/timer to check it.
    -jiw
     
  15. Richard H.

    Richard H. Guest

    Darren,

    You are correct that it takes details to provide a useful answer. Based
    on the broad question originally asked, the URL I provided should have
    met your needs. Perhaps if we understood why you didn't find what you
    needed there, more accurate responses might be possible.

    If you work with engineers much, you'll appreciate that people very
    often ask for the wrong thing - by challenging questionable requirements
    the true specs become known, often hugely affecting the complexity
    involved. Here, you are asking for a degree of accuracy that is
    difficult to achieve, but you say you won't actually be using it, which
    sounds flawed. (Irrespective of the event frequency in the DUT, if you
    are only capturing one-second granularity, more accuracy is wasted.)

    So, you're wasting everyone's time (including yours) looking for a
    solution that won't meet your needs? If you really want nanosecond
    accuracy, we can guide you to a solution that'd give you that, but not
    if you don't ask.

    If you would be less defensive about the requirements and share more
    about your desired goal, you might get help in meeting it - the volume
    of responses here demonstrates folks' willingness to help. We don't
    need you to divulge your experiment, but significant requirements would
    be nice (budget, size, weight, power, connectivity, inputs, outputs,
    skillset), along with some tolerance for validating the potentially
    difficult specs.


    All that said, have you considered the overly simple solution of
    software on a PC? It may be difficult to get better than 18.2ms
    resolution from the system clock, but that is very close to your stated
    requirement, and an RTC clock card would be easy enough to add.

    Then, use SNTP to frequently check an atomic source and factor the drift
    into the local clock's readings. (Or ditch the local clock entirely and
    just make an SNTP/Daytime query of an atomic clock at the time you want
    a reading - the accuracy can be calc'd as good as 1/250 sec.) Plus,
    this is easily extensible to integrate with an event log, rather than
    using a manual process.

    Of course, there's no knowing if this will meet your other unstated
    requirements, so perhaps it was a waste of time to share this idea?

    Richard
     
  16. Guest

    If, even with expert help, a problem appears to be hard or expensive to
    solve, change the problem. Every engineer has done that at least one but
    probably several times...
     
  17. 2.com

    2.com Guest

    You will waste a lot less of everyone's time if you just go ahead
    I said in my very first post that I was looking for an electronic timer
    that is accurate to within 1/60th of a second over the course of 6
    hours. Then the thread turned into questions concerning my project and
    assumptions as to why what I ask for wasn't logical.
    I did previously say: "But of course that kind of timing is not humanly

    possible with any kind of consistency."
    I'm aware of the consistency of the game hardware. And this project
    can't involve tapping into the games clock.
    The problem is the criticizing of my needs and the suggestion of
    alternatives by those unfamiliar with the project. The initial question
    was simple, and I thank those who gave me their best answers.
    I'm just looking for a timer to click off every second on it's display,
    and with the accuracy I mentioned. I know nothing about how to build
    anything, or about the features of the devices in those links.

    Darren Harris
    Staten Island, New York.
     
  18. 2.com

    2.com Guest

    I'm not asking for the wrong thing. The requirements are only
    "questionable to someone not familiar to with what I am trying to do. I
    never said that I will not be using the accuracy I am searching for.
    And I think it has already been established that the kind of accurate
    timer I need doesn't exist(or no one here knows of one).
    Who said that I'm looking for a solution that won't meet my needs?(And
    I only need 1/60th of a second acccuracy).
    All this is unecessary info for a timer with a simple read-out. There
    are no other rquirements than what I stated.
    Again, I need only 1/60th of a second accuracy, and the reference point
    will be from "start".
    Yeah. I guess I'll have to look elsewhere.

    Thanks.

    Darren Harris
    Staten Island, New York.
     
  19. 2.com

    2.com Guest

    The problem is getting a timer.

    Darren Harris
    Staten Island, New York.
     
  20. 2.com

    2.com Guest

    I've already simplified the timer requirements so as to target part of
    my "problem".

    Darren Harris
    Staten Island, New York.
     
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